This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Specific Aims The Overall Goal of these studies is to investigate the processes of neovascularization of ocular tissue. The hypothesis for these studies was that co-culture of retinal and endothelial (EC) cells in three-dimensional culture models will enhance neovascularization by modulating VEGF isoforms through the up-regulation of HIF1a or NFkB expression. The original specific aims are to: 1. Assess the phenotypic (morphological and biochemical) characteristics of retinal progenitor cells and endothelial progenitor cells maintained, alone or in co-culture, in the horizontally rotating bioreactor (HRB); 2. Determine whether hypoxia enhances neovascularization in this model by regulating HIF1a expression; 3. Evaluate the role of HIF1a and NFkB in regulating the expression of VEGF isoforms by cells subjected to cycles of hypoxia and normoxia. Specific Aim #1 was modified after Year 01 to using Transwell contacting and non-contacting co-cultures instead of the HRB systems. This was done because of a number of technical issues that we found with the HRB system, which precluded its continued use. During Year O2, Specific Aims #2 and 3 were combined and a new Specific Aim developed for Aim #3. This Aim is as follows: New Aim #3: to examine the modulation of growth factor expression by mouse endothelial progenitor cells (MEPC) treated with retinoic acid (RA), under normoxic and hypoxic conditions.